The present invention relates to a method and an apparatus for treating high pressure particulate material.
More particularly, the invention relates to a method and an apparatus for pneumatic conveying of particulate material containing reaction products of a high pressure reactor, by using gas exiting the reactor as a carrier gas, from a supply vessel at a pressure of at least two bar to a receiving vessel at a considerably lower pressure, by using an apparatus comprising a conveyor line and a collecting vessel between the conveyor line and the receiving vessel.
It is generally known to convey solid, powdered or granular material by a pneumatic conveyor system. When transported pneumatically, solid material is conveyed in a tubular conveyor line entrained with the carrier gas flowing therein. Pneumatic conveyance is possible for diluted suspensions, whereby a relatively large quantity of gas conveys a relatively small volume of solid material, or for denser suspensions, whereby a relatively small quantity of gas conveys a relatively large volume of solid material.
Pneumatic conveyance is normally performed by feeding superatmospheric carrier gas to a conveyor line or by providing a low pressure in the receiving vessel in the latter end of the conveyor line. Pneumatic conveyance is especially applicable in situations where the supply vessel is for some other reason at a higher pressure than the receiving vessel. Thus, it could be possible to utilize the gas in the supply vessel for conveying particulate material and it is not necessary to separately arrange a carrier gas supply or pressure difference between the vessels.
U.S. Pat. No. 4,699,210 discloses a system to convey fly ash from a pressurized fluidized bed boiler separated by its particle separator in such a way that the material to be conveyed is led from the bottom portion of the separator to an ash container through a conduit in which its flow direction is sharply changed a repeated number of times. Every change of direction consumes energy, however, whereby the pressure of the flue gas conveying the ash is reduced gradually on its way from the particle separator to the ash container.
Another drawback in this conveyor system is clogging of the conveyor line at its sharp bends, especially if the ash temperature decreases close to the dew point temperature of the carrier gas. To prevent clogging of the line, the ash is conveyed as a thin suspension, whereby the flow rate of the gas needs to be high enough, at least 10–15 m/s. This results, however, in a high consumption of the carrier gas and thus, increases the energy consumption substantially. In addition, the high flow rate can cause strong erosion, especially at the bends of the line where the flow direction changes.
U.S. Pat. No. 4,877,423 discloses a two-stage pneumatic system applicable to conveying and cooling high pressure fly ash, at the first stage of which system, where flue gas is used as a carrier gas, the pressure is reduced only slightly, typically only 0–3 bar. In the end section of the first stage is arranged a precipitator to separate flue gas from ash, and a high pressure supply tank for the ash. Subsequent to the supply tank, the system comprises a lock tank separated by a valve, in which tank, the pressure can be reduced to a level required by the further transport and final cooling of the ash.
The disclosed arrangement with a separate precipitator and two tanks is, however, quite complicated and expensive. Furthermore, the ash discharge of the separator, treating the entire ash quantity and having no longer any carrier gas flow, has a tendency to get clogged up, if the ash is adhesive at least to some extent. This also prevents the ash from being efficiently cooled at the first stage.